Re: [Qemu-devel] qemu drive-mirror to rbd storage : no sparse rbd image

[Alexandre DERUMIER <aderumier@odiso.com>]

>>What is the source format? If the zero clusters are actually unallocated in the
>>source image, drive-mirror will not write those clusters either. I.e. with
>>"drive-mirror sync=top", both source and target should have the same "qemu-img
>>map" output.

Thanks for your reply,

I had tried drive mirror (sync=full) with

raw file (sparse) -> rbd  (no sparse)
rbd (sparse) -> rbd (no sparse)
raw file (sparse) -> qcow2 on ext4  (sparse)
rbd (sparse) -> raw on ext4 (sparse)

Also I see that I have the same problem with target file format on xfs.

raw file (sparse) -> qcow2 on xfs  (no sparse)
rbd (sparse) -> raw on xfs (no sparse)


I only have this problem with drive-mirror, qemu-img convert seem to simply skip zero blocks.


Or maybe this is because I'm using sync=full ?

What is the difference between full and top ?

""sync": what parts of the disk image should be copied to the destination;
  possibilities include "full" for all the disk, "top" for only the sectors
  allocated in the topmost image".

(what is topmost image ?)


----- Mail original -----

De: "Fam Zheng" <famz@redhat.com>
À: "Alexandre DERUMIER" <aderumier@odiso.com>
Cc: "qemu-devel" <qemu-devel@nongnu.org>, "Ceph Devel" <ceph-devel@vger.kernel.org>
Envoyé: Samedi 11 Octobre 2014 09:01:18
Objet: Re: [Qemu-devel] qemu drive-mirror to rbd storage : no sparse rbd image

On Wed, 10/08 13:15, Alexandre DERUMIER wrote:
> Hi,
>
> I'm currently planning to migrate our storage to ceph/rbd through qemu drive-mirror
>
> and It seem that drive-mirror with rbd block driver, don't create a sparse image. (all zeros are copied to the target rbd).
>
> Also note, that it's working fine with "qemu-img convert" , the rbd volume is sparse after conversion.

What is the source format? If the zero clusters are actually unallocated in the
source image, drive-mirror will not write those clusters either. I.e. with 
"drive-mirror sync=top", both source and target should have the same "qemu-img
map" output.

Fam

>
>
> Could it be related to the "bdrv_co_write_zeroes" missing features in block/rbd.c ?
>
> (It's available in other block drivers (scsi,gluster,raw-aio) , and I don't have this problem with theses block drivers).
>
>
>
> Regards,
>
> Alexandre Derumier
>
>
>